We designed a prospective study to evaluate the ability of dimercaptosuccinic acid cortical scintigraphy and ultrasonography to detect renal parenchymal lesions in children with pyelonephritis. One hundred eleven patients 1 week to 16 years of age (median 5.5 months) with a urine culture positive for pathogens were included in the study; cortical scintigraphy and ultrasonography were repeated in 25 children after a mean follow-up of 10.5 months. Cortical scintigraphy showed renal changes in 74 children (67%), and ultrasonography showed renal changes in 39 (35%) (p < 0.001); results of the two examinations were discordant in 49 patients (kappa = 0.19). Children more than 1 year of age had a higher incidence of renal lesions than did younger children (85% vs 66%; p = 0.04). The presence of inflammatory signs (erythrocyte sedimentation rate or C-reactive protein) had an 89% sensitivity and a 25% specificity in identifying renal lesions. Among children with renal changes, vesicoureteric reflux was present in 39%. At follow-up examination, 16 children (64%) had scars. Thus we found a high incidence of renal involvement in children with pyelonephritis. We found that cortical scintigraphy is more sensitive than ultrasonography in detecting renal changes, and we believe that it should be added to the initial examination of children with suspected pyelonephritis.